The adjective offhand describes a remark or comment that is made without previous thought or preparation. If you are at a wedding, you may want to make a few offhand but nice remarks about the newlyweds.
As an adjective, offhand can mean careless, brusque, or inconsiderate. You may frequently have to remind young children that offhand comments about people's looks or intelligence can hurt their feelings. Offhand can also be used as an adverb, meaning without thought or planning. You may not be able to say offhand, but do you have any idea how many people are in your class at school?